Field of the Invention
The present invention relates to a transdermal sensor, especially to a transdermal sensor obtain physiologic data by measuring the concentration of hypodermal target molecules.
Description of the Related Art
Tissue fluid is mainly contained in subcutaneous tissue and includes amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts and waste products from the cells. Moreover, the tissue fluid is also the major communication channel for cell and blood. The concentrations of the various components in the tissue fluid are useful for determining user's physiological conditions.
The medicine will be slowly released over a long period in tissue fluid when the patient takes or injects the medicine. The concentration variation of medicine in the tissue fluid is continually monitored during development of medicine and clinical experiment. Therefore, the tissue fluid is commonly sampled to further examine or analyze in medical treatment of patient.
The commercially available physiological examination instruments generally withdraw tissue fluid by using a needle piercing through stratum corneum. However, the patient may feel painful for this kind of invasive sampling way. Moreover, the patient may be infected by microorganism originally present on epidermis and entering the patient body as the stratum corneum is pierced by a needle. Transdermal sensor with array-arranged microneedles pricking through skin is developed to withdraw tissue fluid in painless and minimally-invasive way.
The array-arranged microneedles of a transdermal sensor can be manufactured with standard semiconductor process such as photolithograph process and etching process. U.S. Pat. No. 7,344,499 discloses a process for manufacturing silicon microneedles. As can be seen from the second paragraph of the twelve column of this patent, firstly a silicon wafer with a first patterned photoresist layer is prepared. Next, a through hole is defined on the wafer by anisotropic etching. Afterward, a chromium layer is coated on the wafer and a second patterned photoresist layer is formed atop the through hole to function as circular etching mask. Next, the wafer is then etched to form outer tapered wall for the microneedles. However, the silicon-based microneedles are brittle and tend to break when the microneedles prick through user's skin.
Alternatively, hollow microneedles with resin barbules are proposed, where the barbules are drilled by laser processing. Firstly, sheet with barbules is formed by extruding polyimide or polyether ether ketone, and then the barbules are drilled by laser to form hollow microneedles. However, the microneedles have compact size such that the barbules may have ragged edge after extrusion. Moreover, it is difficult to form a hollow microneedle with off-axis through hole or central through hole having uniform inner diameter by laser processing.